DESCRIPTION (Investigator's Abstract): The research described in this proposal will test (1) whether embryonic neuronal precursor cells with a common future neuroendocrine phenotype occupy a distinct region of the neural plate and (2) whether these cells are specified to express this fate by neural plate stages. The frog, Xenopus, will be used for this study because it has become the preferred species in development studies, it is accessible for the require experiments and cDNA and antibody probes for several neuroendocrine phenotypes are readily available. The first peptide to be studied is mesotocin, the amphibian homologue of mammalian oxytocin. The adult and tadpole distribution of this peptide and its message in the preoptic region of the hypothalamus has been described already by the applicant. Using heterospecies grafts between X. laevis and X. borealis, which provides a cell autonomous marker for the grafts similar to that used in chick-quail chimaeras, a fate map will be made of the Xenopus forebrain region of the neural plate in order to identify the region that will give rise to the preoptic area of the hypothalamus. very small grafts (25-50 mum on a side) will be used to identify the precursors for mesotocin neurons within the preoptic field. This experiment will demonstrate whether mesotocin neurons descend from a confined cluster of neuroepithelial cells or from a mosaic scattered across the entire field. Mesotocin precursor regions will be transplanted to ectopic regions in the embryos to test whether that phenotype is determined by neural plate stages. Mesotocin precursor regions also will be excised or replaced by other neural plate regions to test whether the location in the neural plate determines this phenotype. It is hoped that these studies may lead to establishing a developmental animal model for some congenital neuroendocrine disorders, such as septo-optic dysplasia.